The present invention relates to a tilting pad type bearing device used in a rotary machine.
In general, in a tilting pad type bearing device as shown in a schematic drawing of FIG. 10, a plurality of pads (tilting pads) 102 are divided in a circumferential direction and angularly movably supported to a bearing housing by pins 103 for supporting a rotary shaft 101. The tilting pad type bearing device has an excellent stability characteristic or the like in comparison with a stationary type bearing in which each pad is securely fixed to the bearing housing. The tilting pad type bearing device has been extensively used as a bearing for a rotary machine such as a large scale steam turbine power generator.
As a lubricating system for the tilting type pad type bearing device, there are provided an oil dipping lubricating system and a nozzle forcible lubricating system. In any lubricating system, holes or orifices for supplying lubricant oil to the bearing portions are arranged between the adjacent pads, and grooves for supplying the lubricant oil thereto are provided on the housing side.
As such a conventional tilting pad type bearing device, a journal type, tilting pad type nozzle forcible lubrication system bearing device will now be explained with reference to FIGS. 3 and 4.
In FIGS. 3 and 4, a rotary shaft 1 is supported by a plurality of tilting pads 2a to 2e arranged in a circumferential direction. Each of the tilting pads 2a to 2e is angularly movably supported on a housing 6 by positioning fixed pins 3a to 3e.
The positioning fixed pins 3a to 3e are fixed at a preselected interval in the circumferential direction inside a circumferential groove 9 of the housing 6. A plurality of oil supply pieces 4a to 4c in which a plurality of orifices 5a to 5c are formed on the lubricant oil inlet side are arranged relative to the rotational direction A of the tilting pads 2e, 2a and 2b located at the bearing portions for supporting almost all of the weight and working force of the shaft 1.
The lubricant oil that has passed through an oil supply port 8 formed on the outer circumferential side of the housing 6 and the circumferential groove 9 and that has been fed at a predetermined pressure difference from the oil supply port 8 is allowed to smoothly flow in the direction of C0, C1, C2, C3, C4, C5 and C6 in this order and is introduced into a lubrication surface of the inner circumferential surface of the tilting pads for supporting the rotary shaft 1. Also, the housing 6 is engaged with an outer casing to define the circumferential oil supply groove 9.
Due to recent tendencies toward high speed properties, compactness and higher performance of the rotary machine, surface pressure of the bearing in such a tilting pad type bearing device has been increased, so that the lubrication surface clearance is decreased, increasing frictional loss. A higher bearing performance is required even in severer conditions. In particular, due to the increase of the frictional loss, the heat load imposed on the tilting pad is increased, so that a metal surface temperature of the tilting pads and an oil film temperature of the lubrication surface are elevated. As a result, there is a greater fear of heat sticking. Also, there is a fear that an unstable vibration would occur due to the viscosity reduction and damping reduction of the lubricant oil due to the temperature elevation.
However, in such a conventional tilting pad type bearing device, the outer circumferential sides (back surface sides) of the tilting pads 2e, 2a and 2b to which a large load is to be imposed tends to come into intimate contact with the housing, stagnating the lubricant oil. As a result, the heat resistance is increased and the heat that has been introduced from the lubrication surface on the inner circumferential surface side hardly leaks away. Therefore, a temperature difference occurs between the inner circumferential surface and the outer circumferential surface of each tilting pad, resulting in the elevation of the metal surface temperature of the tilting pads and the elevation of the oil film temperature of the lubrication surface. Thus, the conventional tilting pad type bearing device has a fatal disadvantage in that it can not be used as the bearing device in a rotary machine having a higher performance.